In The Original Series of the Star Trek universe at least three starships of the Klingon D-7 class were given to the Romulan Star Empire as part of a brief alliance with the Klingon Empire against the Federation. The starship Enterprise as it appeared on Star Trek Star Trek is a culturally significant science fiction television series created by Gene Roddenberry in the 1960s. ... The Enterprise boldly went where no man had gone before. ... This page is about the race. ... Introduction The Romulans, a fictional race in the Star Trek universe, are descended from Vulcans and are characterized as being deceitful, cunning, and treacherous. ... Introduction In the fictional Star Trek universe, the United Federation of Planets is a federation of more than 150 member planets and thousands of colonies, based in the Alpha and Beta Quadrants of the Milky Way galaxy. ...

The Romulans refited the D-7s in their service with cloaking devices. It is unknown what other modifications the Romulans made but the non-canon Starfleet Battles table top wargame and the Starfleet Command PC games inspired by it speculate that the Romulans also equipped these vessels with plasma torpedoes, the highly destructive plasma weapon introduced by the Romulan Bird of Prey. In several science fiction universes, a cloaking device is an advanced stealth system which causes a spaceship to be invisible and extremely difficult to detect with normal sensors. ... In the Star Trek fictional universe, plasma torpedoes are weapons used in starship combat. ...

It is generally assumed that the Klingons acquired their cloaking technology which appeared with the Bird of Prey in Star Trek III: The Search for Spock from the Romulans and that it was in exchange for the starships given to the Romulans as well as warp drives superior to those used by the Romulans previously. Star Trek III: The Search for Spock (Paramount Pictures, 1984; see also 1984 in film) is the third feature film based on the popular Star Trek science fiction television series. ... The Enterprise-D goes into warp. ...

Starfleet Battles speculates that the Romulans purchased more than just D-7 class starships and that Klingon ships with Romulan cloaking devices and armaments were used to supplement the Romulans' powerful but overall inferior vessels such as their Bird of Prey until a new generation of ships built with the new technologies acquired from the Klingons could be fielded in significant numbers.

Romulan D-7 Battlecruisers were distinct from their Klingon counter parts by the addition of a cosmetic red feather pattern on the underside of the main hull.